The present invention relates to a dispersion ink, in particular, an ink suitable for an ink-jet printing method comprising the ejection of ink droplets from a print head. More particularly, it relates to a dispersion ink excellent in not only high-definition print quality but also re-dispersibility.
Since dye-dissolved inks conventionally used for ink-jet recording have defects such as low light-fastness and waterfastness, pigmented inks excellent in lightfastness and waterfastness have come to be used in some cases. The pigmented inks have to contain dispersedwater-insoluble pigment particles and have to be stably storable. For example, Japanese Patent Laid-Open Nos. 62-116678, 1-301760, 2-255875, 4-334870 and 8-209048 disclose water-based pigmented inks.
Japanese Patent Laid-Open No. 59-4665 discloses an ink excellent in long-term storage stability, continuous jet stability, etc. In addition, Japanese Patent Laid-Open No. 8-143804 discloses an aqueous dispersion for bubble jet which permits stable jet in bubble jet recording and is excellent in fixability.
In recent years, with an improvement in ink jet printers, such as an increase of definition, the range of use of ink jet is increased and ink has come to be used in various circumstances. Therefore, it has become necessary to consider conditions of use in severe circumstances, such as temperature cycles, vibration-fastness, etc. Particularly for high-density printing, the particle diameter of a pigment or a disperse dye has to be adjusted to a small value. However, the above references, disclose neither a method for using pigment fine particle with an average particle size of 75 nm or less in ink, nor investigation on the re-dispersibility of a pigment or a disperse dye.